In recent years, expansion of the application field of information systems and development of distributed computer systems have brought drastic increase in the number of hosts managed in a site. This trend raises a problem of increase in the management cost of computer systems. In particular, if storage devices mounted on distributed hosts are individually managed, the storage size required for operation is difficult to be estimated. Accordingly, when the computer system needs to increase the capacity, it is required to individually add storage devices to the hosts. Consequently, the management cost goes up.
To solve this problem, technologies of storage area network (SAN) and network attached storage (NAS) are employed. Both of these technologies aim to consolidate storage devices which are individually owned by distributed hosts; however, these are used in different application fields because of their distinctiveness.
The SAN connects a plurality of storage apparatuses to a plurality of hosts by a network dedicated to communication among the hosts and the storage apparatuses to achieve high-speed and low-latency input/output (I/O). In the SAN, I/O between a host and a storage apparatus is performed by blocks. The block is a management unit for fixed-length data, which is obtained by dividing the whole storage space of a storage apparatus into units having a predetermined size and identified by an address.
A typical application suitable for block-based I/O is database. Consolidating volumes of a plurality of database servers into a single storage apparatus and unifying the management can reduce the management cost of the computer system. In addition, since the SAN is a highly reliable dedicated network to perform efficient communication, it is effective to use the SAN as a communication channel for volume-based data transfer. The volume-based data transfer is used to replicate a volume at a remote storage apparatus for the purposes of backup and disaster planning.
On the other hand, the NAS is a storage apparatus having a file server capability to provide file services to a plurality of hosts in a local area network (LAN). The I/O between the NAS and a host is performed by files. The file is a management unit for variable-length data, which is typically identified by a text identifier. A typical application suitable for file-based I/O is file sharing by a plurality of hosts, which achieves a service that a plurality of web servers distribute the same contents or document sharing by a plurality of office personal computers.
In this way, the SAN and the NAS are technologies that complement each other. Therefore, the following idea comes up: integrating a storage apparatus supporting the SAN and a NAS into a single apparatus will achieve further reduction in the management cost. The technique disclosed in the following PTL 1, US 2005/0172043 A, configures the control program for a storage apparatus so as to control both of the SAN and the NAS; consequently, a storage apparatus supporting both of the SAN and the NAS can be attained. The storage apparatus employing this technique has interfaces for the SAN and the NAS, so that it can allocate the storage space to the SAN and the NAS without restriction.